1. Field of the Invention
The invention relates to an expansion valve as e.g. Used in a refrigeration system of an automobile, including a valve body having a high-pressure refrigerant passage for supplying a high-pressure refrigerant to an evaporator of a refrigeration system, and a low-pressure refrigerant passage for a low-pressure refrigerant discharged from said evaporator, a valve mechanism for regulating a flow rate of the high-pressure refrigerant in the high-pressure refrigerant passage, and a control mechanism having an airtight chamber filled with a temperature-sensing gas, a circular filling hole for filling the temperature.-sensing gas into the airtight chamber, and a steel ball fixed by spot welding in said filling hole for sealing the filled airtight chamber, the control mechanism controlling the valve mechanism in accordance with a change in pressure in the airtight chamber caused by a change in volume of the temperature-sensing gas which is induced by a change in temperature of the low-pressure refrigerant flowing through said low-pressure refrigerant passage, and a control mechanism for such expansion valves.
In a refrigeration system (refrigerating cycle) low-pressure gaseous refrigerant (low-pressure refrigerant) delivered from an evaporator to a compressor is adiabatically compressed by the compressor. The resulting high-temperature, high-pressure gaseous refrigerant is condensed by a condenser by heat exchange to obtain a liquid refrigerant (high-pressure refrigerant). Said refrigerant is adiabatically expanded by means of a restrictor in the expansion valve to obtain a low-temperature, low-pressure atomized refrigerant. Within the evaporator the atomized refrigerant is evaporated by heat exchange with ambient air such that the atomized refrigerant again becomes low-pressure gaseous refrigerant. The quantity of refrigerant supplied to the evaporator is adjusted in accordance with a load condition of the evaporator and by using the temperature of the low-presort refrigerant discharged from the evaporator as a parameter. Said adjustment usually is performed by the expansion valve which may have a design as described above.
The control mechanism of said expansion valve comprises an airtight chamber bounded by a diaphragm and a surrounding metallic rigid wall. A temperature-sensing gas is contained in the airtight chamber. The temperature-sensing gas changes its volume in accordance with the temperature of the low-pressure refrigerant contacting e.g. said diaphragm such that the internal pressure within the airtight chamber also changes. By displacement of said diaphragm said valve mechanism is controlled such that the valve opening degree is varied for flow adjustment.
2. Description of the Related Art
EP 0 846 927 A discloses a method for filing the airtight chamber of a control mechanism of an expansion valve. First a filling hole is cut into a part of the metallic wall of the airtight chamber. Then the temperature-sensing gas is filled through the filling hole. Finally, the filling hole is sealed by a steel pellet having the shape of a steel ball spot-welded into the filling hole, e.g. by electric resistance welding along the contact region between the steel ball and the peripheral upper edge of the filling hole. The steel ball regular spherical surface avoids significant variations of the contact with the filling hole edge such that there is less liability of a poor weld. Nevertheless, stable welding conditions cannot be guaranteed so that frequently a secondary sealing by soldering, has to be provided.
EP 831 283 A discloses an expansion valve, the airtight chamber of its control mechanism being sealed by a metallic plug of tapered shape. The plug is spot-welded to the exterior vicinity of the filling hole to seal the filling hole after filling the airtight chamber with gas. As the filling hole sealed with the tapered plug by resistance welding, and the plug has an inclined position in alignment the angle between the outer surface of the plug and the inner surface of the filing hole varies, possibly causing a poor weld quality as a result of said irregular contact. A poor weld with a gap located inside of the weld (nugget) allows the temperature-sensing gas to seep through or induces crevice corrosion. Therefore, secondary sealing between the plug and the fill hole is performed e.g. by soldering.
It is an object of the invention to provide an expansion valve and a control mechanism of the kind a disclosed using a steel ball for sealing the filling hole allowing the achievement of high sealing reliability by e.g. resistance welding. If the ratio D/d between the inner diameter D of the filling hole and the outer diameter d of the spherical surface of the steel ball is set to 0.6 to 0.85, a weld or nugget uniformly can be formed by electric welding over the entire circumference around the contact portion between the steel ball and the filling hole. This improves the reliability of sealing the filling hole. Furthermore, since no small gap can be formed at the contact region between the steel ball and the filling hole edge crevice corrosion can be reliably prevented.
The same positive result is achieved if the steel ball is spot-welded to the filling hole upper edge such that the angle between a line passing through the center of the steel ball and the center of the filling hole and a straight line passing through the center of the steel ball and a point at which the spherical surface of the steel ball touches the upper edge of the filling hole is set between 37xc2x0 and 58xc2x0.
Furthermore, it is of advantage for the quality of the sealing formed by the spot welding if the steel ball spot-welded into the filling hole is sunk during welding and by applied pressure by a depth into the filling hole which is adjusted to about 0.3 mm+/xe2x88x920.1 mm. This measure reliably prevents the formation of even the smallest gap in the contact region.
For a control mechanism for different types of expansion valves it is of advantage to seal the filling hole of the metallic wall of the airtight chamber filled with gas by a steel ball spot-welded into the filling hole with a ratio between the inner diameter D of the filling hole and the outer diameter d of the spherical surface of the steel ball being set in a range between 0.6 to 0.85. Said ration assures a high sealing reliability without the need of additional or supplemental sealing e-g- by soldering.
If the ratio D/d is smaller than 0.6, this leads to the effect that the steel ball is positioned as if it would be placed on a flat object, and the edge of the filling hole is pushed downward, as shown in FIG. 6, such that the nugget formed by welding fails to be formed around the contact area between the steel ball and the filling hole edge, making it difficult to uniformly seal the filling hole. If D/d was larger than 0.85, this could lead to the effect that the edge of the filling hole is pushed out upwards as shown in FIG. 8, such that the nugget fails to form around the pressure-applied region.